Encyclopedia · supplement
Capsaicin and isoflavone (oral)
One 2007 Japanese study found more hair growth in people taking oral capsaicin plus soy isoflavone than placebo, but it was never replicated, and capsaicin applied directly to follicles in the lab does the opposite.
What it is
A combination of capsaicin (the heat compound in chili peppers) and soy isoflavone, taken by mouth. The trial used capsaicin 6 mg/day and isoflavone 75 mg/day for five months (Harada 2007).
How it works
Capsaicin activates the TRPV1 receptor on sensory nerves, releasing a signal called CGRP, which raises IGF-1. Isoflavone increases CGRP production. In mice the pair raised dermal IGF-1 and sped regrowth, and mice lacking CGRP did not respond to capsaicin (Harada 2007).
What the studies show
- In a placebo-controlled human study of 48 people over 5 months, hair growth was judged improved in 20 of 31 on treatment versus 2 of 17 on placebo (p<0.01), and plasma IGF-1 rose. The abstract does not describe how growth was scored or the type of alopecia, so outcome quality is unclear. Harada 2007
- In human scalp follicles in organ culture, capsaicin acting on TRPV1 inhibited hair shaft growth, induced catagen and raised TGF-beta2. Bodo 2005
- A systematic review of 30 supplement studies listed capsaicin-isoflavone among the higher-quality studied supplements, with rare and mild adverse effects. Drake 2023
How it's used in studies
Capsaicin 6 mg/day with isoflavone 75 mg/day by mouth for 5 months.
Side effects and safety
Capsaicin can cause stomach upset or burning; the systematic review reports mild effects overall. Isoflavones are phytoestrogens, which matters for people with hormone-sensitive conditions or pregnancy.
Bottom line
Limited evidence: one positive human study, small and unreplicated. Do not apply chili to the scalp, because the follicle-culture data suggest direct activation can push follicles into catagen. Discuss with a doctor.
Fun facts
Capsaicin is a hair-growth inhibitor when applied directly to cultured human follicles (Bodo 2005), yet an oral version was reported to help, through an indirect nerve-based mechanism.
Studies 3
Harada N et al. Administration of capsaicin and isoflavone promotes hair growth by increasing insulin-like growth factor-I production in mice and in humans with alopecia. Growth Horm IGF Res. 2007
Tested: oral capsaicin 6 mg/day with isoflavone 75 mg/day vs placebo
Result: Hair growth was judged improved in 20 of 31 on treatment vs 2 of 17 on placebo (p<0.01); plasma IGF-1 rose.
Read the study ↗Bodo E et al. A hot new twist to hair biology: involvement of vanilloid receptor-1 (VR1/TRPV1) signaling in human hair growth control. Am J Pathol. 2005
Tested: capsaicin acting on TRPV1
Result: Capsaicin inhibited hair shaft growth, induced catagen and raised TGF-beta2.
Read the study ↗Drake L et al. Nutritional supplements for hair loss: a systematic review. JAMA Dermatol. 2023
Tested: oral supplements including apple nutraceutical and capsaicin-isoflavone
Result: Apple nutraceutical and capsaicin-isoflavone were among the supplements with higher-quality evidence; adverse effects were rare and mild.
Read the study ↗Related
- Red ginsengRed ginseng and red ginseng oil sped hair regrowth in mice and stimulated cultured papilla cells, but no controlled human trial of ginseng alone for hair loss exists.
- Green tea EGCGEGCG, the main green tea catechin, grew human hair follicles in a dish, but there is no good human trial of it alone for hair loss.